Method of producing quenched and tempered hollow steel structural members of polygonal cross section

ABSTRACT

Method of producing quenched and tempered hollow steel structural members of polygonal cross section includes the steps of hot rolling a hollow steel tube, austenitizing the tube, water quenching it, reheating the tube to a tempering temperature just below the lower critical transformation temperature, and rolling the tube to the desired polygonal cross section while holding the temperature of the member at the tempering temperature.

United States Patent [191 Brunko Dec. 18, 1973 [54] METHOD OF PRODUCINGQUENCHED 2,256,455 9/1941 Crawford l48/l2.4 AND TEMPERED HOLLOW STEEL2,748,039 5/1956 Adams et al |48/I2.4

STRUCTURAL MEMBERS OF POLYGONAL CROSS SECTION [75] Inventor: Wade D.Brunko, Library, Pa. [73] Assignee: United States Steel Corporation,

Pittsburgh, Pa.

[22] Filed: Sept. 25, 1972 [21] Appl. No.: 291,854

[52] US. Cl. 148/12.4 [51] Int. Cl C21d 9/08 [58] Field of Searchl48/l2.4

[56] References Cited UNITED STATES PATENTS 2,222,263 ll/l940 Nelsonl48/l2.4

Primary ExaminerW. W. Stallard Att0rneyRalph H Dougherty [57] ABSTRACTMethod of producing quenched and tempered hollow steel structuralmembers of polygonal cross section includes the steps of hot rolling ahollow steel tube, austenitizing the tube, water quenching it, reheatingthe tube to a tempering temperature just below the lower criticaltransformation temperature, and rolling the tube to the desiredpolygonal cross section while holding the temperature of the member atthe tempering temperature.

8 Claims, No Drawings 1 METHOD OF PRODUCING QUENCHED AND TEMPERED HOLLOWSTEEL STRUCTURAL MEMBERS OF POLYGONAL CROSS SECTION within the temperingtemperature range; and g. Allowing the resulting product to be aircooled. The chemical composition of the steel in the tube may be anysteel which is suitable for the production of This invention relates tohollow steel structural tub- 5 q n h and tempered ubes. A Suitablecomposition ing, and more particularly t nch d d t d is asilicon-aluminum killed steel, having a composition structural steeltubing of polygonal cross section such bf about 020% Carbon, t-45%rhahgahese and 006% as square or rectangular. Tubular structural stcclspro- Vahadhlrh- This steel composition is martehsitic and cessed in thismanner developed high yield strengths hibits g weldabihtyand hightensile strengths, together with high notch l0 Austehittzihg isaccomplished at a temperature toughness at l tempetatures greater thanthe A temperature of the steel in the tube.

Heretofore, structural steel tubing of polygonal cross For t steels,this means a temperature greater than sections has been produced in oneof two ways. In the 155001: but will usualty be r about 16000}? to aboutfi method, a Substantially round tube iS f d by 1750F. Preferably, theaustenitization is carried out in hot rolling in a tube-mill, which tubeis formed into the a gas'fired furhaee in ah excess air atmosphere r adesired cross sectional dimensions and shape by passsuffieteht time bassure uniform heating of the tubeing it through a squaring pass afterthe round tube has water qttehehmg ts aeeemphshed by Passing the tubebeen formed. The squaring or sizing operation is carthrough a sertes ofp y quench rthgs to Provide 100% i d out at a temperature of from aboutllOOO to surface coverage of the tube circumference The tube 1500F. Inthe second method, the tube is hot rolled in is quenched to atemperature of about 1500b, but y a conventional manner, then reheatedto about be quenched to y temperature below 2000K 1300F-.,- and passedthrough a sizing mill to form the The tempering temperature is j abovethe stress b i a polygonal crosslsootion H treatment of relievingtemperature and just below the lower critical the finished shapes hasresulted in distortion of the flat transformation temperature of thesteel that is, l faces of the shapes beyond acceptable commerciallimbelow the el temperature For most steels, pe g i Thus, the physicalproperties such as Strongth and will be carried out at a temperaturebetween about toughness of these tubes are limited to those properties 11500b and 1225OF- The tube ls pe for a Perted which can be attributed tochemical composition alone. suffieteht to bring the tube to a uhttbrmtempering US Pat. No. 2,748,039 teaches a method of producing P r aquenched and tempered pipe of round cross Section The tube 15 rolled tothe des red polygonal cross secwhich requires additional smallreductions to be made such as a round'ebrhereft q rbuhdjeorhered afterthe quench and temper process to remove minor rectangle or y desiredCI'OSS b Whlle distortions caused n within the tempering temperaturerange. This 18 nor- This invention is predicated upon my development ofa e wtth a 512mg haylhg a number or stands a weldable waterquenched andtempered structural wtth sqbarrhg'bassestube of polygonal cross sectionto meet the demand for h shapes Pr y thrs rhethbd e free ofhigherstrength structural materials with superior notch ht a e highhbteh toughness, g ytetd strength toughness properties and ultimateStrength.

Accordingly, it is the principal object of this inven- To llustratethepresent invention, two steels having tion to provide a method ofproducing quenched and 40 ehethleat ebrhpbsttlbhs as shown Table etempered hollow Stool Structural members of polygonal melted in anelectric furnace and rolled into 10 inch dlcross section having highyield strengths, and excellent emetet b rouhde h were Subsequentlyrolled notoh toughness and elongation propertios into 10 ea inch outsidediameter seamless tubes, half of It is a further object of thisinvention to provide a each eerhbbsrttbh hafthg'three'elghths lrlehwalls a method of producing dimensionally Correct holloW half havingone-half inch walls. The lower vanadium Stool structural members contenttubes were austenitized at l600F, and the The method-of the inventionconsistS higher vanadium tubes at l650F, in a walking beam H lli a llSteel b i substantially furnace for 100 minutes per inch of wallthickness. This oval or circular cross section by any conventional wasfollowed y P y quenching with q h water at tube rolling method; atemperature of about 92F. The one-half Inch wall b, A i i i h b tubeswere quenched at a speed of 26 ft. per minute 0. Water quenching thetube to about 150F; and the three-eighths inch wall tubes at 36 ft. permind. Reheating the tube to a temperature above the tubes were regrbupedand some were stress relieving temperature and below the Ac Pered at andm at l2 25F. All tempering temperature; .was for 72 minutes totalfurnace time, after which the Tampering th b i h tempering temperatureround tubes were formed into square tubes at the temrange; peringtemperature in a five-stand sizing mill having f. Rolling the tube tothe desired polygonal cross secsquaring P The final tubes Were a d t airtion while holding the temperature of the tube e001- 0 w *7 TABL E l CMn P S, Si Al V Cu Ni Cr M0 N2 night No. l .22 1.49 0.011 0.019 0.450.064 0.037 0.01 0.16 0.08 0.01 0.008 Ingot N0. 2 .22 1.51 .009 .019 .47.067 .071 .01 .16 .03 .01

Table 2 shows the mechanical properties from two as-rolled tensile testsand tests from each tube quenched and tempered according to thisprocess. From this data, it is clear that 75,000 psi minimum 4 above thestress relieving temperature and below the Ac temperature; e. temperingsaid tube at said tempering temperature; f. rolling said tube to thedesired polygonal crossyield strength may be attained in all wallthicknesses to 5 section while within said tempering temperatureone-half inch. range; and

TABLE 2 Longitudinal strip tensile Temper Yield Ultimate Elong.

Pipe N0. Austenilizing temperastrength strength in 2" Y|eld and endComposition Wall temperature ture (F.) (psi) (psi) tens|le lE-S 0.04 V0.500" As-rollcd 68,490 98,480 32.0 0.70 2ES.. 74,070 103,790 28.5 .72lA-N. 88,630 102,980 30.0 .86 1BS... 89,770 103,300 27.5 .87 lC-N..79,400 94,350 34.0 .84 1DS.. 80,300 95,460 35.0 .84 lE-N.. 86,090100,680 33.0 .86 lG-S... 82,590 94,200 35.0 .88 ll-N 80,800 95,220 35.0.85 2A-N. 98,070 111,420 30.0 .88 2BS..... 102,990 1 14,480 29.0 .902C-N. 91,420 104,790 31.0 .87 2DS.. 95.440 100,260 32.5 .95 2ES.....90,670 106,680 31.0 v .85 2G-N. 84,590 101,200 33.5 .84 21-S... 85,360102,610 36.0 .83

b. austenitizing said tube at a temperature greater than the Atemperature of the steel in said tube; c. water quenching said tube; d.reheating said tube to a tempering temperature V g. air cooling saidtube.

2. A method according to claim 1 wherein said austenitizing temperatureis above 1550F.

3. A method according to claim 2 wherein said austenitizing temperatureis from about 1600F to about 1750F.

4. A method according to claim 1 wherein said tube is water quenched toa temperature below about 200F.

S. A method according to claim 4 wherein said tube is water quenched toa temperature of about F.

6. A method according to claim 1 wherein said tempering temperature isfrom about 1150F to about 1225F.

7. A method according to claim 1 wherein said polygonal cross-section isa round-cornered rectangle.

8. A method according to claim 1 wherein said polygonal cross-section isa round-cornered square.

2. A method according to claim 1 wherein said austenitizing temperatureis above 1550*F.
 3. A method according to claim 2 wherein saidaustenitizing temperature is from about 1600*F to about 1750*F.
 4. Amethod according to claim 1 wherein said tube is water quenched to atemperature below about 200*F.
 5. A method according to claim 4 whereinsaid tube is water quenched to a temperature of about 150*F.
 6. A methodaccording to claim 1 wherein said tempering temperature is from about1150*F to about 1225*F.
 7. A method according to claim 1 wherein saidpolygonal cross-section is a round-cornered rectangle.
 8. A methodaccording to claim 1 wherein said polygonal cross-section is around-cornered square.